1. Field of the Invention
The present invention relates to an electric generating unit as a substitute for a vehicle battery and, more particularly, to an electric generating unit as a substitute for a vehicle battery, which is independently provided for the operation of an electronic device for a tire pressure monitoring system (TPMS), for example, which is newly governed by laws and regulations.
2. Description of Related Art
In general, an automobile is equipped with electronic devices and requires power supply to drive these electronic devices. Recently, since the application of electronic devices to the automobile is rapidly increased, the quantity of electric wires for the power supply to the electronic devices is also increased. For example, a tire pressure monitoring system (TPMS) is governed by laws and regulations, and a power generating device capable of generating electrical energy by external vibration or pressure is provided to operate the TPMS.
FIG. 1 is a diagram illustrating a concept of generating electricity in a conventional piezoelectric generating apparatus in accordance with a conventional art, in which a steel ball beats piezoelectric ceramics plates disposed on both sides thereof by external vibration.
Referring to FIG. 1, piezoelectric ceramics plates 1 are disposed on both sides of a cylindrical container closed at both ends and, when a steel ball 4 beats these piezoelectric ceramics plates 1, electricity is generated. A buffer plate 3 is attached on one sidewall of the container 8 using an adhesive 6, and one piezoelectric ceramics plate 1 is attached to only the center of the buffer plate 3 using the adhesive 5. Same as above, the other piezoelectric ceramics plate 1 is attached on the other sidewall of the container 8, and thereby the piezoelectric ceramics plates 1 face each other. A protective plate 2 is fixed at the center of each of the piezoelectric ceramics plates 1 facing each other. A pipe 7 is arranged between both of the piezoelectric ceramics plates 1, and the steel ball 4 which can roll freely is provided in the pipe 7.
The piezoelectric ceramics plate 1 is formed by joining two plate-like piezoelectric ceramics elements 1a and 1b having the same shape (same material and same thickness) with inverted polarity of the dielectric polarization. Since the piezoelectric ceramics elements 1a and 1b formed in the same manner are joined to each other, a flexural vibration is caused on the junction surface as the central point (position where it does not expand and contract). In this case, if the ceramics element 1a on one surface expands, the ceramics element 1a on the other surface contracts, and the polarities of output voltages are the same direction. The two piezoelectric ceramics elements 1a and 1b are connected in series in the electricity generation structure.
When the flexural vibration is generated centering on the junction surface, both operations of expansion and contraction are performed on one piezoelectric ceramics element 1a or 1b and the generation of electricity is effectively performed without cancellation of the polarization. The current generated as electrical energy is obtained through lead wires 9.
In this case, the two piezoelectric ceramics elements 1a and 1b are stacked; however, each piezoelectric ceramics element 1a or 1b can be formed in a stacked manner. In this stacked structure, a plurality of thin piezoelectric ceramics plates (in this case, polarities of the polarization are the same) are joined and stacked, and thereby one piezoelectric ceramics element 1a or 1b is formed.
The reason that the piezoelectric ceramics plate 1 is fixed to the center of the buffer plate 3 using the adhesive 5 is to prevent the vibration of the piezoelectric ceramics plate 1 from decreasing. When the piezoelectric ceramics plate 1 vibrates, a member supporting the piezoelectric ceramics plate 1 is a factor of reducing the vibration of the piezoelectric ceramics plate 1. To remove the factor of reducing the vibration, the piezoelectric ceramics plate 1 is in a free state using the buffer plate 3.
Since a natural vibration of the piezoelectric ceramics plate 1 is maintained for a long time by using the buffer plate 3, the efficiency of electricity generation is improved. The buffer plate 3 also absorbs the impact applied to the piezoelectric ceramics plate 1. The protective plate 2 is made of metal, synthetic resin, or the like, and it protects the piezoelectric ceramics plate 1 from the beating of the steel ball 4.
If the piezoelectric generating apparatus is arranged under predetermined motional conditions that utilize wind, wave or human action, the steel ball 4 rolls up and down and beats the right and left piezoelectric ceramics plates 1 so as to apply impact energy by the collision. Then, the vibration is generated on the piezoelectric ceramics plates 1, the piezoelectric ceramics plates 1 repeatedly expand and contract, and therefore the piezoelectric ceramics plates 1 generate alternating current electricity.
The above-described piezoelectric generating apparatus can generate large energy with a relative small force; however, the performance is significantly reduced by high frequency vibration and, especially, abrasion occurs in the region where the steel ball beats, which affects the durability. Moreover, concave and convex portions are formed by contaminants on the inside surface of the pipe, where the steel ball moves, thus obstructing the movement of the steel ball.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.